May 13, 2011

A Construction Perspective on the Impact of National Electrical Code (NEC) and National Electrical Safety Code (NESC) on Wind and Solar Power Facilities

Adhering to Code and the Dual Role of Wind and Solar Power Facilities

Wind and solar power plants may be subject to different standards and interconnection requirements, depending on their size, geographic location, interconnection point, and other factors. The IEEE standard C2- National Electrical Safety Code (NESC) applies to electric supply facilities, while the NFPA 70- National Electrical Code (NEC) governs utilization facilities. According to Article 11 of the NESC, “The NESC covers utility facilities and functions up to the service point. The NEC covers utilization wiring requirements beyond the service point.”

Utility-scale wind and solar power plants are unique in that they contain elements of both generation and utilization facilities and are often owned by a non-utility. The dual role of renewable power facilities can result in uncertainty about which code applies under specific circumstances. To further complicate matters, each state enforces and issues its own regulations for code compliance, and a state may have several different entities that define the work, typically split between utility generation projects and private residential, commercial, or industrial projects.

NESC and NEC Codes Govern Utility and Non-Utility Compliance

The NESC is the code that a utility must follow as related to its generating facilities, transmission lines, and distribution systems (i.e., the high voltage work) and the NEC is the code that a non-utility must comply with, usually associated with a public or private building facility (i.e., the low voltage work). A utility is exempt from following the NEC except for installations such as office buildings, warehouses, machine shops, etc. that are not an integral part of a generating plant, substation, or control center. A large- scale wind or solar power plant does not necessarily fit this black and white description.

Ultimately, the wind or solar facility must comply with regulations specified by the Occupational Health and Safety Administration (OSHA), and a majority of installations have chosen to comply with both the NESC and the NEC, as this gives the best opportunity for compliance.

Defining the AHJ and Code Requirements Early-On

The Authority Having Jurisdiction (AHJ) is defined in the NEC as “An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or procedure.” Therefore, it is imperative for the developer, owner, or builder of a wind or solar power plant to determine early in the process who comprises the AHJ and what they require for code enforcement.

Many wind and solar power projects are located in remote locations and an AHJ may not be directly involved with the project, or if involved, may not have the experience necessary to perform the required inspections. Many of the local inspectors, or AHJ’s, responsible for wind power plants only have experience with low voltage work. In these cases, they will either choose to ignore the high voltage work or may cause hardship for the wind power project by requiring something non-standard to distribution level voltages.

The following is a statement from the inspection authority for Minnesota regarding the NESC: “Most work under the jurisdiction of the NESC in Minnesota is exempt from licensing and inspection requirements and therefore the NESC is minimally referenced by the ‘inspection’ department”. This is just one example where the high voltage work on a wind or solar power plant may present challenges to fully understanding what one is required to consider in the design of a wind or solar facility.

The 2011 edition of the NEC includes a section on wind turbine installations, but is only valid for turbines of 100kW or less which is not meant for large-scale wind projects. Requirements for solar power plants has had its own dedicated section since the 1984 edition, but only addresses the low voltage work.

Interpretation of Code

The following are a few examples of how code can be interpreted differently by project, inspector, and state:

• International Building Code (IBC) certification of an electrical control building within a substation. This requirement will vary by state. Since these structures are more commonly designed for a utility, they have traditionally been exempt from any specific certifications. As a private entity, even if building for a utility, they may not necessarily be exempt. Some engineers have labeled these as ‘electrical equipment enclosures’ in lieu of a building to help guide the AHJ to a more favorable ruling.
• Grounding of collection systems
  • Both the NESC and NEC require multi-grounded systems to have the concentric neutral wires grounded not less than four times per mile. Engineers in the industry are divided on whether this is required for medium voltage wind collector systems, with varying reasons for its exemption.
  • At least one turbine manufacturer requires a separate trench ground from the concentric neutral wires. However, there are differing opinions within the industry for turbine suppliers that do not specifically require this.
• Grounding of turbine foundations. Should the rigorous “step and touch” safety considerations as defined in IEEE 80 be a requirement for wind projects? IEEE 80 is written specifically for substations.  Other tall steel structures and padmounts located in public places do not design for this situation, and there are poorly grounded padmounts in residential locations with higher step touch potentials than at a typical wind turbine generator foundation.
• Use of copper clad steel for ground wire instead of solid copper. Copper clad steel ground wire is becoming more popular due to the rising cost of copper and its susceptibility to theft while being prepared for installation or after installation. Copper clad steel ground wire is not a recognized conductor in the NEC but is allowed per the NESC.
• DLO cable used for the low voltage cabling between the padmount transformer and the wind turbine generator.  Per the 2011 edition of the NEC, the termination lug combinations with the conductor must be specifically listed for the application. The finely stranded DLO low voltage cable commonly used between the wind turbine generator and the step-up transformer outside the tower.
• Color-coding of conductors. The NEC has strict requirements for color-coding conductors, and these color combinations may not be similar to what utilities use inside substations. The designer should be cognizant of these color combinations.
• Conduit selection. Conduit greater than 6” diameter is commonly used in routing the ‘homerun’ collection feeders into the substation and used for bores. The NEC does not recognize PVC or HDPE (high density polyethylene) conduit in trade sizes larger than 6”.
• Medium voltage cable that is not UL listed. Until recently, very few cable manufacturers of URD cable (used as the 34.5kV conductor for collection systems) were UL listed and approved by the NEC. URD is a common direct burial cable used by utilities for many years and rarely used by private entities. Since there was not a demand for a NEC approved cable, many manufacturers did not get the URD cable UL listed. However, the majority of URD cable is now UL listed and does satisfy the NEC.

Arc Flash Considerations

Regulations governing arc flashes are another electrical issue in wind and solar power construction that warrant further discussion. The most basic approach would be to apply the NESC arc flash rules to the medium voltage collector system and the NFPA 70E rules to the inside of the turbine tower. This would provide good coverage of the inside equipment and the proper approach to the medium voltage collection system and substation. This approach will also help define the proper personal protective equipment (PPE) for both working situations.

Summary

Without clear and defined standards and codes to follow in the design and construction of wind and solar power plants, it is critical to define the approach, codes, and standards that will be applied during the early stages of project development. Most importantly, the AHJ must clearly be defined and ground rules established for acceptable practices. It is important to note that there could be local jurisdictional rules, ordinances, or laws that may supersede both the NESC and NEC. This would also include identifying the version of the code that has been adopted by a particular state or province since this may not be the latest released version.

The IEEE Power and Energy Society (PES) Wind Power Coordinating Committee has established a subcommittee called the “Integration of Renewable Energy into the Transmission and Distribution Grids” and subsequent working groups to address these issues with the intention of establishing standards for the design of wind and solar power facilities. The purpose of these working groups is to help define the proper standards that should be applied when designing and constructing wind and solar power projects.

 

***************************

 

GENERAL INFORMATION

The NESC is revised every 5 years. The purpose of the NESC is the practical safeguarding of persons during the installation, operation, or maintenance of electrical supply and communication lines, equipment, and associated work practices employed by a public or private electric supply, communications, railway, or similar utility in the exercise of its function as a utility.

It covers similar systems under the control of qualified persons, such as those associated with an industrial complex or utility interactive system. It is not intended as a design specification or as an instruction manual.

What Isn't Covered

NESC rules do not cover installations in mines, ships, railway rolling equipment, aircraft, or automotive equipment, or utilization wiring except as covered in Parts 1 and 3. For building utilization wiring requirements, see the National Electrical Code.

How the NESC differs from the National Electric Code® (NEC®)

The NEC, NFPA-70, addresses proper electrical systems and equipment installation to protect people and property from hazards arising from the use of electricity in buildings and structures. This includes:

• Installations of electric conductors and equipment within or on public and private buildings or other structures, including mobile homes, recreational vehicles, and floating buildings; and other premises such as yards, carnivals, parking lots, and industrial substations.
• Installations of conductors and equipment that connect to the supply of electricity.
• Installations of other outside conductors and equipment on the premises.
• Installations of optical fiber cable.
• Installations in buildings used by the electric utility, such as office buildings, warehouses, garages, machine shops, and recreational buildings that are not an integral part of a generating plant, substation, or control center.